"Somehow I ended up surrounded by people that love me and care for me and will do anything for me. It's a good feeling," Simon explained to Shriver, recalling when he received his diagnosis in 2012. "That's called happiness."

It's a heartbreaking situation, but one that Simon is content with. "A lot of it is selfish," he explained. "I get to watch these animals that have been in concrete bunkers their whole life, I get to watch them take their first steps on grass, I get to fly my friends out." As for why he made the decision to donate his fortune, Simon added: "[The animals are] dependent on us for that and so I feel that it's my responsibility to speak for those who can't speak for themselves."